1. Field of the Invention
The present invention relates to a stable syrup which contains the highest possible amount of trehalose, more particularly, to a high trehalose content syrup in which trehalose is dissolved in an amount that exceeds its saturation concentration in water along with other saccharide(s) and which syrup is free of or substantially free of crystallization of trehalose, and to uses thereof. The present invention also relates to a method for preventing the crystallization of trehalose in a high trehalose content syrup, an agent which contains as an effective ingredient a reducing and/or a non-reducing saccharide for preventing the crystallization of trehalose, and a method for preventing the crystallization of trehalose characterized by a step of dissolving the agent in a high trehalose content syrup.
2. Description of the Prior Art
Trehalose, .alpha.,.alpha.-trehalose, has long been known as a non-reducing saccharide which is composed of glucose units. It is described in "Advances in Carbohydrate Chemistry", published by Academic Press, USA, Vol.18, pp.201-225 (1963) and in "Applied and Environmental Microbiology", Vol.56, pp.3,213-3,215 (1990) that trehalose is widely distributed in microorganisms, mushrooms and insects in an extremely small amount. Non-reducing saccharides like trehalose neither cause the amino carbonyl reaction with amino acid containing substances such as amino acids and proteins nor deteriorate amino acid containing substances, and therefore they can be used and processed with these substances without causing unsatisfiable browning reaction and deterioration. As a result, there was the expectation that the production of trehalose would be established on an industrial scale.
In conventional preparations of trehalose, microorganisms are utilized as disclosed in Japanese Patent Laid-Open No.154,485/75, and as disclosed in Japanese Patent Laid-Open No.216,695/83, maltose is converted into trehalose by using maltose- and trehalose-phosphorylases in combination. However, the former is not suitable for the industrial production of trehalose because the amount of trehalose in microorganisms as a starting material is usually less than 15 w/w % (the working "w/w %" will be abbreviated as "%" in the present specification, unless specified otherwise), on a dry solid basis (d.s.b.), and the extraction and purification steps are complicated. The later has the following demerits: (i) Trehalose is formed via glucose-1-phosphate so that maltose as a substrate could not be used at a relatively-high concentration; (ii) The enzymatic reaction systems of these phosphorylases are reversible reactions, and this renders the yield of the objective trehalose relatively low; and (iii) It is substantially difficult to keep the reaction systems stable and to continue these enzymatic reactions smoothly. Thus, it has not yet been actually used as an industrial-scale preparation.
As regards the preparation of trehalose, it is reported in the column titled "Oligosaccharides" in the chapter titled "Current Status of Starch Application Development and Related Problems" in "Food Chemicals", No.88, pp.67-72 (August, 1992) that "In spite of a wide applicability of trehalose, an enzymatic preparation thereof via a direct saccharide-transfer reaction or a hydrolytic reaction has been recognized to be scientifically almost impossible." Thus, an enzymatic preparation of trehalose using starch as a material has been deemed to be scientifically impossible.
It is known that partial starch hydrolysates such as liquefied starches, cyclodextrins and maltooligosaccharides which are prepared from starch a material usually have a reducing end-group as an end unit. These partial starch hydrolysates are referred to as "reducing partial starch hydrolysates" in the present specification. The reducing power of reducing partial starch hydrolysates is generally expressed by "DE" (dextrose equivalent), based on a dry solid (d.s.b). It is known that, among reducing partial starch hydrolysates, those with a relatively-high DE have generally a relatively-lower molecular weight and viscosity and a relatively-higher sweetening power and reactivity, and readily react with substances having amino groups such as amino acids and proteins to cause undesirable browning, smell and quality deterioration.
These properties of reducing partial starch hydrolysates vary depending on their DE values, and the relationship between reducing partial starch hydrolysates and their DE is very important. It has been even believed in this field that it is impossible to break off the relationship.
To solve this problem, the present applicant disclosed in Japanese Patent Application No.349,216/93 that a novel non-reducing saccharide-forming enzyme which forms non-reducing saccharides, having a trehalose structure as an end unit, from one or more reducing partial starch hydrolysates selected from those with a DE of at least 3 (the enzyme will be referred to as "non-reducing saccharide-forming enzyme, throughout the present specification"). The applicant established a process for producing non-reducing saccharides having a degree of glucose polymerization of at least 3 and having a trehalose structure as an end unit, and a process for producing trehalose from these saccharides by using the non-reducing saccharide-forming enzyme.
The present applicant also disclosed in Japanese Patent Application No.79,291/94 that a novel trehalose-releasing enzyme which specifically hydrolyses the linkage between trehalose and other molecules in non-reducing saccharides having a degree of glucose polymerization of at least 3 and having a trehalose structure as an end unit (the enzyme will be referred to as "trehalose-releasing enzyme", throughout the present specification), and established a process for producing trehalose with an increased yield by using the above two novel enzymes in combination. The present applicant further disclosed in Japanese Patent Application No.144,092/94 that a maltose-trehalose converting enzyme which directly converts maltose into trehalose, and established a process for producing trehalose in a relative-high yield from maltose produced from reducing partial starch hydrolysates.
During studying the uses of trehalose, the present inventors noticed that in addition to hydrous- and anhydrous-crystalline trehaloses, the tankage, trucking and pumping transportation of high trehalose content syrups are greatly required. However, the water solubility of trehalose is relatively low, and unsaturated trehalose solutions are susceptible to bacterial contamination because of their relatively low concentration, while supersaturated trehalose solutions are considerably poor in stability at ambient temperature and susceptible to crystallization and precipitation of hydrous crystalline trehalose, readily resulting in loss of their satisfactory homogeneous free-flowing ability and in a serious damage when stored in tanks or transported by pumps. Therefore, stable trehalose syrups with the highest possible content of trehalose are strongly required.